Video: How Leaping Fish Species Left the Water — For Good

Using high-speed video, researchers have revealed the biomechanical tweaks that allow a little-known fish called the leaping blenny to thrive on land.

Propelled by a twisting motion that turns their tails into springboards, leaping blennies have colonized rocky intertidal areas across the South Pacific. Closely related species still live in the ocean, but leaping blennies only go back by accident.

“None of the blennies were observed voluntarily entering the water during low or high tide,” wrote Temple University biomechanicist Tonia Hsieh in a study published June 18 in Public Library of Science One.

Tsieh is one of a handful of researchers to study leaping blennies, formally known as Alticus arnoldorum. They’ve escaped scientific attention in part because blennies live among rocks buffeted by large, violent waves. It’s a niche shared only with limpets and crabs, which could explain the evolutionary pressures favoring A. arnoldorum‘s terrestrial migration.

In the latest study, Hsieh studied leaping blennies and five closely-related species. Each can breathe through blood vessel-rich skin while out of water, allowing them to survive indefinitely if intermittently splashed, but only A. arnoldorum and one other blenny, Praealticus labrovittatus, venture onto land.

Hsieh used high-speed video and force-measuring plates to compare the locomotion of the different species. She found that A. arnoldorum and P. labrovittatus begin their leaps by curling their bodies into a C-shape. It’s a shape seen often in the aquatic fish world as a reflexive response to danger, preceding a burst of escaping speed. The two blennies have brought it under intentional control.

Hsieh also found that A. arnoldorum has literally added a twist, rotating its tail fin sideways for extra push. This added boost likely explains its wholly terrestrial tendencies; P. labrovittatus, with its basic C-shape, is merely amphibious, and still returns regularly to the ocean.

“The terrestrial blennies have co-opted this for movement on land,” Hsieh said.

Hsieh next plans to study the genetic relationships between the species, determining how the terrestrial blennies evolved and perhaps guessing how they’ll evolve in the future. She also wants to study the blennies’ impressive climbing abilities, which seem to involve adhesive mucus and suction-forming fins, allowing them to climb slippery, vertical surfaces.

“People say that a fish out of water is a dead fish, and that’s not necessarily true,” said Hsieh.